1. Field of the Invention
The present invention relates to a cell balance device for achieving a cell balance of secondary batteries connected in series and a battery system including the cell balance devices, and more particularly, to a cell balance device capable of improving speed for achieving a cell balance with an inexpensive configuration and a battery system including the cell balance devices.
2. Description of the Related Art
FIG. 7 illustrates a circuit diagram of a conventional cell balance adjusting circuit. A cell balance device including the conventional cell balance adjusting circuit is provided with an assembled battery portion, in which a plurality of secondary battery cells (hereinafter, referred to as cells) 401 to 406 as basic components are connected in series, and switches 411 to 462 each having one contact connected to a node between the cells. The other contact of each of the switches 411, 421, 431, 441, 451, and 461 is connected to one electrode of a capacitor 407 which is a voltage hold device. The other contact of each of the switches 412, 422, 432, 442, 452, and 462 than the one contact on the cell side is connected to the other electrode of the voltage hold device 407. A load circuit or a charging circuit 408 is connected across the assembled battery.
Open/close signals for the respective switches are connected so that the switch 411 and the switch 412 may operate simultaneously. Signals are similarly connected so that the switch 421 and the switch 422, the switch 431 and the switch 432, the switch 441 and the switch 442, the switch 451 and the switch 452, and the switch 461 and the switch 462 may be open/closed simultaneously each as a switch of a set of corresponding two switches. The switch open/close signals sequentially turn ON/OFF the connections in the order of ON/OFF of the switch 411 and the switch 412, ON/OFF of the switch 421 and the switch 422, ON/OFF of the switch 431 and the switch 432, ON/OFF of the switch 441 and the switch 442, ON/OFF of the switch 451 and the switch 452, and ON/OFF of the switch 461 and the switch 462. Such open/close signals that continuously perform repetitive switch open/close operations by returning to the first ON/OFF operation of the switch 411 and the switch 412 after finishing turning ON/OFF the switch 461 and the switch 462 are connected to control portions of the respective switches.
Next, an operation is described. The switches are scanned sequentially in one direction so as to be switched over while forming parallel connections between the series-connected adjacent cells and the voltage hold device 407, to thereby form parallel connections sequentially between all the series-connected cells and the voltage hold device 407. After completion of the formation of parallel connections with all control target cells in the assembled battery, the same switching operation is repeatedly performed from the first cell, thereby adjusting a cell balance.
The switches 411 and 412 are configured to receive signals for simultaneous open/close operation, and the switch 421 and the switch 422 are also configured to be open/closed simultaneously. The same is applied to the other switches, and the simultaneous open/close operation is performed in each combination of the switch 431 and the switch 432, the switch 441 and the switch 442, the switch 451 and the switch 452, and the switch 461 and the switch 462. After the open/close operations are advanced from the switch 411 and the switch 412 and then open/close of the switch 461 and the switch 462 is completed, open/close of the switch 411 and the switch 412 is started again to repeat those operations sequentially. In the case where all the cells maintain a balanced state in which the cell voltage are equal to one another, no electric charges are exchanged between the voltage hold device 407 and the cells. The individual cell states are not affected at all by the open/close operations of the respective switches. In the case where a balance is lost among the cells, such balance adjusting function is exhibited.
In the conventional technology, however, only one voltage hold device (capacitor) is provided for the number of cells to be balanced, thus causing a problem that the battery system has low balance performance (low balance speed). In addition, when the number of secondary batteries to be connected to the cell balance device increases, a higher voltage is applied to the cell balance device, and the cell balance device therefore needs to be manufactured through high voltage process, thus causing another problem of increased cost.